Assessment of the Functional State of Microcirculation of the Blood in Human Tissues by Methods of Speklemetria and Doppler Flowmetry

Abstract

Based on an analytical method for estimating parameters of a speckle structure formed by multiple scattered light in multilayer biological tissue such as human skin at visible wavelengths - the near-IR range, using known solutions of the radiation transfer equation in biological tissue and linking the theory of light propagation in a scattering medium to coherence theory built a mathematical model of the propagation of laser radiation in biological tissue. Using the mechanics of multiphase media, blood for mathematical modeling was initially considered a two-phase viscous suspension consisting of two phases: a parietal and an axial plasma layer with erythrocytes. The blood flow through vessels was modeled taking into account a number of anomalous effects (rheological properties) of blood flow: the Farus effect, the non-erythrocyte parietal plasma layer, the Farus — Lindquist effect, and the blunt blood velocity profile. The characteristics of microcirculation in human tissues were investigated by a non-invasive speckle-optical method using the Speckle-Scan device. In the frequency range of 40-1000 Hz, the power of the spectrum, the average frequency of the spectrum, and the root-mean-square velocity of the particles were determined. At the same time, skin microhemodynamics was investigated using Doppler ultrasound (USDG) using the Minimax-Doppler-K device. The mean linear and average volumetric blood flow rates were determined from the average velocity curve. The data obtained by the USDG and the Speckle-Scan devices were compared with each other and with a mathematical model of the propagation of laser radiation in the microcirculation channel. It was established that the parameter “average frequency of the spectrum” largely reflects the perfusion, and the area under the spectral curve reflects the capacity of the capillary bed. It has been established that the average power of the spectrum of fluctuations of the intensity of scattered radiation after decompression of a vessel increases by about 15 % in comparison with the normal state. The autocorrelation functions of the field fluctuations are obtained when the particles are scattered back at different pressures after decompression of the brachial artery into a difference in the time periods for registering changes. The slope of the autocorrelation function, depending on pressure, can be used to diagnose the tone (elasticity) of blood vessels. Methodical approaches are proposed for evaluating the obtained data in order to verify speckle measurements using the widely used Doppler flowmetry technique.